Ekman presents similarities for 14 colors which are based on a rating by 31 subjects where each pair of colors
was rated on a 5-point scale (0 = no similarity up to 4 = identical).
After averaging, the similarities were divided by 4 such that they are within the
unit interval. Similarities of colors with wavelengths from 434 to 674 nm.
References
Ekman, G. (1954). Dimensions of color vision. Journal of Psychology, 38, 467-474.